argus/src/lib/chain.js

// Chain queries for the registration flow: address -> UTXOs, broadcast, lookup.
// libauth only (no node builtins) so it runs in the browser and in Node.

import {
  cashAddressToLockingBytecode,
  lockingBytecodeToCashAddress,
  sha256,
  hash160,
  binToHex,
  hexToBin,
} from "@bitauth/libauth";

// Electrum indexes by "scripthash": sha256(lockingBytecode), byte-reversed, hex.
export function lockingBytecodeToScripthash(lockingBytecode) {
  return binToHex(sha256.hash(lockingBytecode).slice().reverse());
}

export function addressToLockingBytecode(address) {
  const r = cashAddressToLockingBytecode(address);
  if (typeof r === "string") throw new Error(`bad address "${address}": ${r}`);
  return r.bytecode;
}

export function addressToScripthash(address) {
  return lockingBytecodeToScripthash(addressToLockingBytecode(address));
}

// Re-encode any cashaddr as its token-aware ("token address") form, which is
// what a certificate output must be sent to. Same locking bytecode either way;
// the flag only tells wallets the address is safe to receive CashTokens on.
export function toTokenAddress(address) {
  const bytecode = addressToLockingBytecode(address);
  const prefix = String(address).includes(":") ? address.split(":")[0] : "bchtest";
  const r = lockingBytecodeToCashAddress({ bytecode, prefix, tokenSupport: true });
  if (typeof r === "string") throw new Error(`cannot token-encode "${address}": ${r}`);
  return r.address;
}

export function stripTokenAddress(address) {
  const bytecode = addressToLockingBytecode(address);
  const prefix = String(address).includes(":") ? address.split(":")[0] : "bchtest";
  const r = lockingBytecodeToCashAddress({ bytecode, prefix, tokenSupport: false });
  if (typeof r === "string") throw new Error(`cannot encode "${address}": ${r}`);
  return r.address;
}

// Fetch spendable outputs for one address.
// Returns [{ txid, vout, satoshis: bigint, address, lockingBytecode, token? }]
// `token` is present (and the UTXO is NOT safe to spend as plain change) when
// the output carries CashTokens.
export async function getUtxos(electrum, address) {
  const lockingBytecode = addressToLockingBytecode(address);
  const scripthash = lockingBytecodeToScripthash(lockingBytecode);
  const list = await electrum.call("blockchain.scripthash.listunspent", [scripthash, "include_tokens"]);
  return list.map((u) => ({
    txid: u.tx_hash,
    vout: u.tx_pos,
    satoshis: BigInt(u.value),
    height: u.height,
    address,
    lockingBytecode,
    token: u.token_data
      ? {
          category: u.token_data.category,
          amount: BigInt(u.token_data.amount ?? 0),
          nft: u.token_data.nft
            ? { capability: u.token_data.nft.capability, commitment: u.token_data.nft.commitment }
            : undefined,
        }
      : undefined,
  }));
}

export async function getUtxosForAddresses(electrum, addresses) {
  const out = [];
  for (const a of addresses) out.push(...(await getUtxos(electrum, a)));
  return out;
}

export async function broadcast(electrum, txHex) {
  return electrum.call("blockchain.transaction.broadcast", [txHex]);
}

export async function getTransaction(electrum, txid, verbose = true) {
  return electrum.call("blockchain.transaction.get", [txid, verbose]);
}

/**
 * Who paid us — recovered from the transaction itself.
 *
 * A refund needs a destination, and the only address a payer has *provably*
 * controlled is the one they spent from: to create the input they signed with
 * its key. So rather than asking (and being told a typo, or nothing at all),
 * read the compressed public key straight out of the P2PKH unlocking script and
 * derive the address from it.
 *
 * A standard P2PKH unlocking script is exactly two pushes:
 *     <push sig (71-73 bytes DER, or 65 schnorr)> <push pubkey (33 or 65)>
 * so the last push is the public key. Anything else — multisig, a covenant, a
 * non-standard script — returns null rather than a guess, because refunding to a
 * wrong address is worse than not refunding automatically.
 */
export function payerAddressFromInput(scriptSigHex, prefix = "bchtest") {
  if (!scriptSigHex) return null;
  const script = hexToBin(scriptSigHex);
  const pushes = [];
  let i = 0;
  while (i < script.length) {
    const op = script[i++];
    let len;
    if (op >= 0x01 && op <= 0x4b) len = op;
    else if (op === 0x4c) len = script[i++];
    else if (op === 0x4d) { len = script[i] | (script[i + 1] << 8); i += 2; }
    else return null; // opcodes other than pushes -> not a plain P2PKH spend
    if (i + len > script.length) return null;
    pushes.push(script.slice(i, i + len));
    i += len;
  }
  if (pushes.length !== 2) return null;
  const pubkey = pushes[1];
  if (pubkey.length !== 33 && pubkey.length !== 65) return null;

  const r = lockingBytecodeToCashAddress({
    bytecode: Uint8Array.from([0x76, 0xa9, 0x14, ...hash160(pubkey), 0x88, 0xac]),
    prefix,
    tokenSupport: false,
  });
  return typeof r === "string" ? null : r.address;
}

/** The paying address of a transaction, read from its first spendable input. */
export async function payerAddressOf(electrum, txid, prefix = "bchtest") {
  const tx = await getTransaction(electrum, txid, true);
  for (const vin of tx?.vin ?? []) {
    const addr = payerAddressFromInput(vin?.scriptSig?.hex, prefix);
    if (addr) return addr;
  }
  return null;
}

export { binToHex, hexToBin };